Human hepatocellular carcinoma (HCC) is the fifth most common cancer, yet it is among the most lethal cancers world wide because late detection and high frequency of tumor recurrence render current HCC therapy ineffective. We previously showed that mouse hepatocytes deficient (-/-) in the proliferation-specific Forkhead Box ml (Foxml) transcription factor are highly resistant to developing Diethylnitrosamine (DEN)/Phenobarbital (PB) induced liver cancer and that FoxMl transcriptional activity is inhibited by amino acids 26 to 44 from the ARF tumor suppressor. We also developed transgenic (TG) mice in which the Rosa26 promoter was used to drive ubiquitous expression of the human FoxMlb cDNA transgene. We have developed a new mouse model of aggressive metastatic liver cancer. After 33 weeks of DEN/PB exposure. ARF-/- Rosa-26 FoxMlb TG mouse livers are necrotic and develop aggressive HCC that metastasized to the lungs. In Aiml. we propose to further characterize the proliferation, development and metastasis of this aggressive liver cancer and determine whether these hepatic tumors exhibitnecrosis and activation of hepatic Kupffer and stellate cells. In preliminary studies, we pharmacologically reduced Foxml activity in HCC in vivo by subjectingDEN/PB treated wild type (WT) mice to daily injections of a cell penetrating ARF 24 to 46 peptide. After 4 weeks of this ARF peptide treatment. HCC regions display reduced cell proliferation and angiogenesis with a selective apoptosis of HCC. However, whether this ARF 26-44 peptide is also effective in preventing metastasis of liver cancer to the lung remains to be determined. In Aim2. we propose to test the hypothesis that treatment of ARF -/- Rosa26 FoxMlb TG liver tumors with the cell penetrating ARF 26-44 peptide will inhibit HCC growth and lung metastasis. We have developed a new TG mouse line that conditionally expresses activated H-Ras in postnatal hepatocvtes. We will use these mice to examinewhether activated H-Ras stimulates progression of DEN induced liver tumors in both Rosa26-FoxM 1 b TG mice and ARF -I- Rosa26-FoxMlb TG mice and whether the cell penetrating ARF 26-44 peptide is an effective treatment to limit growth and progression of these liver tumors. Completion of the proposed studies will characterize new mouse models of aggressive metastatic liver cancer and determine whether the cell penetrating WT ARF 26-44 peptide is an effective treatment to prevent metastasis of liver cancer to the lung. These studies will facilitate development of a rational design for future translationalresearch in the treatment of human liver cancer with this ARF peptide inhibitor of the FoxMl transcription factor.